1. Field of the Invention
This invention relates to novel target wafers and target wafer assemblies for electronic theft detection systems and more particularly it concerns novel target wafers and fasteners which contain electronic target circuits and which can be temporarily but securely attached to articles of merchandise.
2. Description of the Prior Art
In U.S. Pat. No. 3,500,373 there is described an electronic theft detection system which may be used in a retail store to protect articles of merchandise from theft. As described in that patent, a wafer is provided for each article to be protected. The wafer is a generally flat plastic element which contains a frequency selective electronic circuit and which can be temporarily, but securely, attached to the article. If any article of merchandise, having such a wafer attached to it, is carried through a checkpoint or interrogation zone, such as at or near the store exit, the electronic circuit in the wafer will react with an electromagnetic interrogation field in the checkpoint zone and will cause an alarm to be sounded.
In U.S. Pat. No. 3,911,534 (now disclaimed) there is described a ball clutch type locking mechanism by which a tack-like fastener element can be locked to a wafer containing a frequency selective electronic circuit and which allows the fastener element to be released by application of a magnetic field.
In U.S. Pat. No. 4,187,509 there is described a wafer for use in an electronic theft detection system wherein the wafer comprises a plastic housing formed with internal grooves for supporting a coil in a flat plane and internal support walls for supporting a capacitor. The wafer is also formed on one side with a dome shaped lock housing for mounting a locking mechanism and on the other side with a dome-like projection surrounding a fastener shank opening to accommodate the head of a tack like fastener.
The wafer and fastener constructions of the prior art have proved to be very practical and have been commercially successful. Nevertheless, it has been found that under certain circumstances, by insertion of a prying tool such as a screwdriver under the edge of the head of the tack-like fastener element, enough leverage can be applied on the wafer housing to pry the head and force the fastener shank out of the locking mechanism. Also, it is sometimes possible to apply plier-like cutters to the dome shaped lock housing and, by working at the housing, cut into it sufficiently to disassemble and release the locking mechanism.